In many stepping motor application the objective is to move an inertia load such as a print disk accurately from one position to another in a minimum of time. Such applications usually require a velocity profile having a much acceleration as possible that is compatible with the shortest low-speed homing time and yet allow the motor to be detented at the desired position. In other words, overshoot or undershoot of the targe position is to be avoided.
Whereas in many printers, the disk is rotating while printing, in a start-stop disk priner designed for a high print rate, the disk is rotated to a new position and brought to rest between hammer firings. In moving the disk to select the desired character, the number of increments necessary for moving the disk to the target position is calculated for the motor and these data in turn determine the number of acceleration signals to be applied to control the motor. The control data are usually maintained in a storage device from which the appropriate values are extracted. With this control technique, the stored data are frequently not optimized because of variable operating conditons or motor characteristics. For example, the power supply voltage, ambient temperature, or mechanical friction may either vary during operation or from one mechanism to another. Fixed numbers of acceleration, deceleration or stop signals for motor control then become causes for inefficient operation. When fixed values are stored, frequently changes are not easily made in the data and a service call or extensive time is required to alter the control data.
It is accordingly a primary object of this invention to provide a control system for stepping motors in which control data can be altered in accordance with the actual operating conditions encountered.
A further object of this invention is to provide apparatus to move a stepping motor as rapidly as possible from an initial position to a target position while considering prevailing extraneous conditions.
Yet another object of this invention is to provide a stepping motor control circuit that changes the proportion of acceleration steps to total steps according to actual operating conditions.
A still further object of this invention is to provide a stepping motor control system in which the homing distance is used to determine the number of acceleration signals applied to the motor during a future stepping sequence.
A still further object of this invention is to provide a stepping motor control circuit in which the number of acceleration signals for a stepping sequence are recalled from a storage device and then modified or left unchanged for subsequent sequences as a result of actual performance.